Oscillator power output maximizing system



AMPLITUDE OR FREQUENCY Jan. 3, 1950 E. MILL-ER 2,493,011

OSCILLATOR POWER OUTPUT MAXIMIZING SYSTEM Filed Oct. 8, 1947 F/GI/ 27 2Sheets-Shet 1 EMSED TO CUT-OFF a 4.3 a FIG. 2

REPELLER VOLTAGE lNVENTO/P SEM/LLER V UWM ATTORNEY Jan. 3, 1950 s. E.MILLER 2,493,011

OSCILLATOR POWER OUTPUT MAXIMIZING SYSTEM Filed Oct. 8,-1947 2Sheets-Sheet 2 T0 LOAD muse sews/r11 5 %-'-76' anscron Ill,

lNl/E/V TOR 5.5. MILLER A TTOR/VEY.

Patented J an. 3, 1950 OSCILLATOR POWER OUTPUT MAXIMIZING SYSTEM StewartE. Miller, Jackson Heights, N. Y., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication October 8, 1947, Serial No. 778,627

Claims.

This invention relates to a system for holding the power output of anoscillator or amplifier automatically at a maximum value and isparticularly applicable to an oscillator of a type in which the poweroutput has a maximum value at an intermediate point in the voltage rangeof a potential upon one of the electrodes of the oscillator.

Electron velocity variation oscillators including reflex oscillators andmagnetrons are examples of oscillators to which the invention isapplicable. In the case of the reflex oscillator, the power output goesthrough a maximum value at a definite optimum voltage of the repellerelectrode. In the case of the magnetron, the power output is a maximumfor a particular value of the potential difference between the anode andthe cathode.

In accordance with the invention, a small alternating potential isimpressed upon the control electrode of a space discharge device to becontrolled, for example the repeller electrode of a reflex oscillator,causing the power output to fluctuate continuously within narrow limits.The power fluctuations of the oscillator may advantageously be amplifiedand are then impressed upon a detector together with an alternatingcurrent of steady amplitude having a definite phase relation to thealternating current which is impressed upon the control electrode toproduce the power variations. The amplitude of the response produced bythe detector is dependent upon the phase relationship between the twoalternating current components which are superimposed upon the detector,and for that reason the detector is referred to as being phasesensitive. On one side of the optimum control electrode potential, thetwo alternating current components are in aiding phase relationshipwhile on the other side of the optimum point the two components are inphase opposition. The detected current is impressed upon the controlelectrode in such polarity as to tend to restore the system to maximumamplitude of oscillation whichever way the control electrode potentialmay vary from the optimum point.

The invention is more fully described hereinafter in conjunction withthe accompanying drawings, while the scope of the invention is definedin the appended claims.

In the drawings, Fig 1 is a schematic circuit diagram of an embodimentof the invention as applied to a refiex oscillator of the electron ve- 2locity variation type. Fig. 2 is a diagram useful in explaining theoperation of the invention and Fig. 3 is a circuit schematic diagram ofan embodiment of the invention as applied to a magnetron.

Referring to Fig. 1, there is shown therein a reflex oscillator I0comprising a space discharge device including a cavity resonator ll, anoutput coupling loop l2 therein, a cathode l3 and a repeller electrode[4. The output coupling loop is connected to any suitable load through alead I5. A relatively low frequency source It, such as a SO-cyclegenerator or power line, is shown supplying two separate circuits eachof which advantageously includes a trans-' former. One such transformerl'l supplies a relatively low potential output through a potentiometerI8 and a condenser l9 to the repeller electrode l4. A second transformer20 supplies a relatively large alternating potential to the anode of atriode 2l which is biased to cut-off to operate as a detector. A battery22 or other source of potential for accelerating electrons is connectedin a circuit between the cavity resonator H and the cathode l3, thecircuit including a resistor 23. The end of the resistor 23 remote fromthe battery 22 is connected through a condenser 24 to the grid of atriode 25 which triode together with a similar triode 26 comprises analternating current amplifier 63 the output of which is connectedthrough a condenser 21 to the control grid of the detector triode 2|. Acathode resistor 28 is included in the cathode circuit of the tube 2|and across the resistor 23 is advantageously connected a lowpass filter6| comprising series resistors 29, 33 and 3| and shunt capacitors 32, 33and 34. The terminals of the capacitor 34 are connected across the gridcathode circuit of a direct current amplifier tube 35 in the anodecircuit of which is an anode load resistor 36. The terminal of theresistor 36 adjacent to the anode of the aube 35 is connected through alead 37 to the repeller M of the oscillator ID. A supply battery 33 isconnected between the anode and cathode of the tube 35, in a circuitthat includes a cathode rheostat 39 and the load resistor 36. A circuitfor measuring the power output of the oscillator is provided, comprisinga rectifier 4| and a resister 42 connected in shunt to the load. Acrystal rectifier is well suited for this purpose.

In the operation of the system of Fig. l, the application of the battery22 between the cavity resonator II and the cathode [3 together with theapplication of a suitable potential upon the control repeller l4produces oscillations in the cavity resonator H in known manner, whichoscillations may be supplied to any desired load through the coupling l2and the lead 15. The low frequency current, for example 60 cycles, fromthe generator l6, impressed upon the repeller electrode I4 through thetransformer l7, potentiometer l8 and condenser l9 causes a periodicslight fluctuation in the repeller voltage which in turn causes powerfluctuations of small magnitude in the oscillations in the cavityresonator II and causes corresponding potential fluctuations in theresistor 23. The fluctuations of potential in the resistor 23amimpressed upon the alternating current amplifier 60 through the couplingcondenser 24. An amplified replica of the fluctuations in the resistor23 is impressed upon the grid of the detector 2| through the couplingcondenser 21. the low' frequency alternating current is impressedthrough the transformer 2!] upon the anode of the detector 23 throughthe lead 40. The detected current passed by the tube 2! through thecathode resistor 28 thereof, is dependent upon theph'ase relationshipbetween the alternating-current components impressed upon the grid and.anode respectively. Maximum detected current is obtained when the gridand anode components are in the same phase and minimum is obtained whenthese two components are directly opposed in phase. The current obtainedin the *cathode resistor 28 is filtered in the low-pass filter 6| comrising the Another component of sultant variation in the crystal currentand the elements 29 to 34 inclusive, resulting in a relaresistor 36through the tube 35 to impress a direct current component upon therepeller electrode I4 through the lead 31. The amp1itude of the directcurrent in resistor 36 is conveniently adjustable by-varying therheostat 39.

The control action of the system of Fig. 1 may be explained withreference to Fig. 2 which is a diagram showing'various quantitiesassociated with the oscillator I 0 and their variation as a function.ofthe voltage upon the repeller electrode 14. The'abscissae' in Fig. 2are values of repeller voltage'and the ordinates are amplitudes ofcertain currents in the system or the frequency of the-system as thecase may be. The curve 43' represents the current-in the rectifier 4| asa-fu'nction of'the voltage on the repeller electrode 14. The curve 44represents the current through the resistor 23 between the cavityresonator Hand the cathode 13. The curve 45 represents the variation ofthe frequensy of the oscillator 'I0 with change of repeller voltage. Thecurve 46 represents the low frequency alternating wave impressed uponthe repeller electrode 1-4 from the potentiometer l8 assuming-thattherepeller voltage is on the left-hand'side of the optimum repellervoltage as indicated in'Fig. '2. Curve 4'! shows the resultingfluctuations in the crystal current in response to the alternationsshown in the curve 46 and the curve 48 shows the correspondingvariations in the current from the cavity resonator to the cathode.- .Itwill be noted that when the fluctuation of the curve 46 is towardtheright, the curves and 48' are each in the upper portion of its cycleof variation while when voltage back to the optimum value.

curve 5| represents the resulting variation in the cavity resonator tocathode current. It will be noted that when the curve 49 goes to theright, the curves 50 and 5| go through the lower portion of their cyclesand when the curve 49 goes to the left'the curves 50 and 51 go throughthe upper portion of their cycles. Accordingly it is evident thatthesame phase of impressed alternating current, shown by either curve 45 orcurve 49, produces one phase of alternating current or the directopposite depending upon which side of the optimum repeller voltage "theimpressed alternating current voltage is applied.

In the system of Fig. 1, the rectified current in the resistor-36 is ofsmall amplitude when the alternating current on the repeller electrodeI4 is operating on the side of the optimum repeller voltage for whichthe grid and anode alternations impressed upon the detector 2| are inopposite phase and the rectified current in the resistor 36 isrelatively large when the repeller electrode voltage is on the otherside of the optimum value, the grid and anode components then being inthe .same phase. It will be noted from Fig. 2 that the closer therepeller voltage approaches the optimum value, the smaller thevariations produced in the curves 4?, 48, 50 and 5| and hence thesmaller the control voltage produced across the resistor 36. Thepolarities in the system of Fig. 1 are so arranged therefore that whenthe repeller voltage departs to one side or the other from the optimumvalue, the resultin detected current produces a change in the repellervoltage in such a direction as to tend to bring the repeller No matterwhich side the departure is made, the correction is'obta-ined, becauseas will be seen from Fig. 2 the systemdiscriminates between departuresto the right and to-the left, the alternating current component being inone phase when the departure is to the left and in the opposite phasewhen the departure is to the right.

Unlike the usual automatic control system the arrangement of Fig. 1 doesnot functionto maintain a constant output but does function to keep theoutput always at the maximum value. If it is desired'to control thefrequency of the system by some sort of frequency control, automatic orotherwise, this may be done by known means and with the system of Fig. lin operation, the power output will be maintained at a maximumregardless of variations in the frequency of the system.

Fig. 3 shows an embodiment of the invention in a system containing amagnetron, wherein 10 is the anode block shown in'cross-section, H isthe cathode also in cross-section, and I2 is an output coupling 100parranged in conventional manner in one of the cavity resonators 13 inthe block 10. A lead 14 connected with the loop-12 is provided forextension to a load circuit of any desired form. A power supply source15 shown as a battery for simplicity is connected with its negativeterminal directly to the cathode ll-and its positive terminal to theanode block through a control resistor 16, a winding 11 of a transformer18 and ground 79, the anode block 10 being grounded. A shunt circuitcomprising a rectifier 80 and a resistor 8| in series therewith isconnected between the lead 14 and ground, thereby shunting the load ofthe magnetron. The terminals of the resistor 8! are connected to theinput terminals of an alternating current amplifier 82, the outputterminals of which are connected to one pair of input terminals of aphase sensitive detector 83. A second pair of input terminals of thedetector 83 are connected across a winding 84 of the transformer 18. Thedetector 83 has a pair of output terminals that are connected across thecontrol resistor 16. A low frequency alternating current source 85,which advantageously comprises a Gil-cycle generator or power line isconnected to a winding 81 of the transformer 18, which winding 81constitutes a primary winding with respect to secondary windings T! and$4.

In the operation of the system of Fig. 3, the application of the battery15 between the anode block 10 and the cathode H of the magnetrontogether with a suitable potential impressed across the control resistor16 by means of the phase sensitive detector 83 produces oscillations inthe magnetron cavity resonators 73 in known manner, which oscillationsare supplied to the load through the loop 12 and the lead 14. The lowfrequency current from the source 85, impressed between the anode l0 andthe cathode ll through the transformer 18, control resistor 16, andground 19, causes a periodic slight fluctuation in the anode-cathodevoltage of the magnetron which in turn causes power fluctuations in theloop 12, lead 74 and the shunt circuit 80, 8| at the same low frequency(GO-cycle) rate. These power fluctuations are demodulated in therectifier 8D, producing corresponding (GO-cycle) fluctuations in thedirect current component of the rectified current in the resistor 8|.The demodulated power fluctuations (GO-cycle currents) are amplified inthe alternating current amplifier 82 and impressed upon the phasesensitive detector 83 along with low frequency (GO-cycle) current fromthe source 85 impressed upon the detector 83 through the transformerWinding 84. The amplitude of the low frequency current from theamplifier 82 varies with power output of the magnetron, becoming less asthe power output approaches a maximum value and changing to the oppositephase when the power output passes through the maximum value. Theamplitude of the low frequency current from the winding 84 is constant.The phase sensitive detector performs the same function as the rectifiertriode 2| in the system of Fig. 1, giving a direct current output whichvaries with the phase of the output of the amplifier 82 and the amountof the departure of the power output of the magnetron from its maximumvalue. The rectified current output of the detector 83 is impressed uponthe control resistor 16 producing therein a potential drop which isimpressed between the anode and cathode of the magnetron in suchpolarity that any change in the power output of the magnetron iscounteracted and the power output is controlled to maintain it atmaximum value at all times.

What is claimed is:

1. A space discharge device having a control electrode, the power outputof which space discharge device goes through a maximum value at anintermediate value in an extended range of pdtential upon said controlelectrode, a phase sensitive detector having an output circuit connectedto said control electrode, a source of variable potential, means toimpress a potential from said source upon said control electrode, meansconnected to said space discharge device for generating a potential thatvaries in accordance with power fluctuations in the output of said spacedischarge device, and means for superposing in the said phase sensitivedetector upon the potential from said source of variable potential thesaid potential which varies in accordance with power fluctuations of thesaid space discharge device in the particular phase relationshiprequired to increase the power output of the said space dischargedevice.

2. A space discharge device having a control electrode upon which avariable potential causes the power output of the device to vary with amaximum power output within the given range of variation of thepotential, a source of variable potential connected to said controlelectrode to produce fluctuations in the power output of the device,means to detect the power fluctuations produced by said variablepotential, a phase sensitive detector for combining a potential fromsaid source of variable potential with the detected power fluctuationsof said space discharge device to produce a detector output potential,and means to impress said detector output potential upon said controlelectrode in proper polarity to increase the power output of the spacedischarge device.

3. An oscillator of a type the power output of which goes through amaximum value at an intermediate value of the potential impressed upon acontrol electrode of the oscillator, a rectifying device, a source ofpotential variations, means to impress potential variations from saidsource upon said control electrode and upon said rectifying device,means to impress a unidirectional potential from said rectifying deviceupon said control electrode, means connected to said oscillator forgenerating a potential variation which follows power variations in theoutput of said oscillator, and means for superposing in said rectifyingdevice the said last-mentioned potential variation upon the saidfirst-mentioned potential variation in the particular phase relationshiprequired to increase the power output of said oscillator.

4. A reflex oscillator comprising a cavity resonator, a cathode, and arepeller electrode, a source of relatively low frequency oscillations, aphase sensitive detector, means connecting said low frequency source tosaid repeller electrode and to said phase sensitive detector, means togenerate a potential which follows the low frequency fluctuations in thepower output of said reflex oscillator due to the low frequencyoscillations impressed upon said repeller electrode, means to impresssaid low frequency potential upon said phase sensitive detector alongwith said low frequency oscillations to produce a potential in theoutput of said phase sensitive detector, and means to impress saidlast-mentioned potential upon said repeller electrode in proper polarityto increase the power output of the reflex oscillator.

5. A reflex oscillator having a cathode, an anode consisting of a cavityresonator, and a repeller, a source of relatively low frequencyoscillations, a detector having an anode, a cathode Title: saikiiresistor connecting the said cavity-res) nator to the cathode: of thereflex oscillator.v

SI-EWART E. MILLER.

REFERENCES. CITED' The folfowing references are of recorcf in the fileof this patenfi:

UNITED STATES. PATENTS 1 Number Name Date 2 404568 Dow July- 23, I9462,4065850' Pierce Sept. 3; 1946

